Friday, July 7, 2017

I find it hard to believe that nearly two months have passed since the 2016/17 academic year drew to a close. I am still pretty amazed by how much I learned in my first year in grad school, and I am eager to continue the learning process next year.

While all my courses ultimately proved to be interesting (and challenging), the highlight of this past academic year was Systems Neuroscience. As its name implies, Systems Neuroscience provided a comprehensive overview of the human nervous system. Even though the pace of the course was sometimes overwhelming, I was rapt by its content.

A significant aspect of the Systems Neuroscience curriculum was neuroanatomy. At the outset of the course, I expected that neuroanatomy would be one of the easier aspects of the course for me. I have long enjoyed studying anatomy and viewing the body 3-dimensionally, which interestingly enough, has become a hallmark of my yoga teaching. As a result, I came to consider my spatial sense to be well developed. As it turned out, neuroanatomy was far and away the most difficult part of the course for me!

Nonetheless, I worked with 3D computer renderings, flashcards and no small amount of hair-pulling to memorize the various vascular structures, brain regions, brainstem nuclei and neural circuitry that was presented in Systems Neuroscience.

As a yoga teacher, I found studying the vascular structures that supply the brain to be particularly interesting. I've long heard of arterial dissection as a potential cause of stroke in yoga practitioners, and now I feel like I have a better understanding of the vital blood supply to the brain.

As you can see in the adjacent diagram, an artery passes through the vertebrae. This artery has the logical name of Vertebral Artery, and is part of the sophisticated blood supply to the brain. As I've mentioned in a previous blog entry, any artery can be damaged by excessive movement. If you consider a wire coat hanger, the wire can be bent a nearly infinite number of times, as long as the bend isn't too great. If the coat hanger is repeatedly bent too far, however, the coat hanger will break.

The arteries aren't likely to break, though they can be damaged by delamination. Consider the adjacent image - the arteries are made up of concentric layers. These tissues are wonderfully robust, though the boundary layers between the layers can potentially be a site of damage. When the boundaries between the layers are damaged by overstretching, there's the potential for an arterial dissection (the proper name for what I'm calling delamination.) The arterial dissection, in turn, can lead to parts of the artery breaking loose... and finding their way upstream into the brain.

Arteries are made up of layers.

The upstream movement of debris is a big problem - ultimately the debris blocks a brain artery, and then that part of the brain is starved for oxygen. This is the essence of a stroke - damage to the brain that's caused by an interruption in blood flow.

For yoga practitioners, I believe that there are two primary points to keep in mind when making decisions about how and what to practice.

Firstly, avoid extreme flexion and extension of the neck. Because the vertebral artery passes through the vertebrae, extreme forward or backward bending can cause the bones to push too hard against the vertebral artery, which can cause damage. Here's what I consider the most important point: those that have loose joints (joint laxity) are capable of pushing their necks deeply into both flexion and extension, and as a result, may increase the risk of making neck movements that could damage the vertebral artery. If you are joint-lax, you'd be wise to limit your extreme movements of your neck.

Secondly, not all arteries are equally resistant to delamination. Those of us with joint-laxity are more likely to have compromised boundary-layer connections, and are at increased risk of arterial dissection. With joint laxity, it's like the glue that holds the various layers together is a little weaker, and the layers are at higher risk to separate. As a result, those of us with joint laxity are at increased risk of boundary layer damage in various tissues such as the skin, veins, arteries, gut, etc. Again, for those with joint-laxity, you need to mindfully resist the Siren's sweet songs that can lead you too deeply into poses.

In summary, arterial dissection is not urban myth - while not common, it does happen to some really nice people that love Yoga. If you have joint laxity (please see prior blogs for more discussion on joint laxity), you are at increased risk of the strokes that can arise from arterial dissection. No need to stop practicing Yoga - simply consider reducing how deeply you move into all your poses. And if nothing else, please be sure not to flex or extend your neck too far!

2 comments:

Thanks for the real science scoop. I've been advocating that people not do big neck circles in part because of that artery, but also (according to articles noted below) because the facet joints in the cervicals can get worn down and ("but wait, there's more!") a nearby nerve in the spinal cord can get impinged.

I don't know anything about the first author, but here's her article on the reasons to expunge neck circles from your practice: http://sequencewiz.org/2014/03/11/neck-circles-can-compress-cervical-nerves-cause-issues/

also Julie Gudmestad warns about neck rolls for similar reasons. https://www.yogajournal.com/teach/how-to-stay-safe-in-neck-rolls-stretches

Welcome to the Alignment Yoga blog, where you'll find yoga articles, videos and audio presentations by Scott Anderson, with an emphasis on how to avoid common mistakes we make doing this ancient practice with our Western bodies and minds.